1. FIELD OF THE INVENTION
The present invention relates to a duct type of air conditioner which adopts a variable air volume control system capable of controlling temperatures in a plurality of rooms independently.
2. DISCUSSION OF BACKGROUND
A conventional duct type air conditioner for a house and the like which can control the temperature in each room independently has operation modes such as an "OFF (stop)" mode, a "heating" mode, a "cooling" mode and a "ventilating" mode. The "ventilating" mode is selected to carry out ventilation between the rooms in a season which does not require cooling or heating. When an external air intake duct is connected to a main duct, external air can be taken into the rooms and cooling by the external air is possible though it is not always enough. In addition, it is possible to equalize by the ventilating operation the room temperatures in the rooms which are different from one another due to conditions such as solar radiation.
In general, the conventional air conditioner carries out the ventilating operation, opening dampers in all the rooms when the "ventilating" mode is selected.
There is Japanese Unexamined Patent Publication No. 31844/1986 as a first prior art reference, which discloses the cooling by external air is positively carried out in times before and behind summer.
In the first prior art reference, the damper in each room is opened or closed depending on whether the room temperature detected by a thermostat is higher or lower than the ventilating air temperature in the duct, in order to make the room temperature approach to a set temperature by use of the ventilating air.
The variable air volume control (hereinbelow, referred to as VAV) system for the duct type of air conditioner is classified into a throttle type and a bypass type. The throttle type is further classified into a, two-position control (on-off control) type and a proportional control 12 in terms of the way to control the damper.
An example of the throttle type of two-position control system is Japanese Unexamined Utility Model Publication No. 81438/1983 as a second prior art reference. The air conditioner as disclosed in the publication carries out the on-off control of the damper to minimize the difference in temperature between an upper portion and a lower portion in the room to be heated, thereby increasing comfort. At the time of heating, the on-off control is carried out so that when the room temperature is lower than a set temperature, the opening of the damper is maximum, when the room temperature is higher than the set temperature, the opening of the damper is minimum, and when the room temperature is approximate to the set temperature, the maximum opening and the minimum opening are repeated in a cycle.
In order to carry out such control, the difference between a detection signal by a room temperature detecting sensor and a detection signal by a room temperature setting device is input to a differential amplifier, the output from the differential amplifier is input with a signal from a pulse generator into an on-off time difference generator to output an on-off control signal to the damper.
Although the total air volume in the duct changes depending on the total opening degrees of the dampers to fluctuate the pressure in the duct, the capacity of an air blower in the air conditioner is controlled based on a detection signal by a pressure sensor to maintain the pressure in the duct constant.
There is Japanese Unexamined Patent Publication No. 119146/1976 as a third prior art reference. It described that electrically powered or electromagnetically powered dampers are arranged in the duct and that the dampers are controlled based on signals from the room thermostats to have a full-open state or a semi-open state so as to regulate the room temperatures. The damper for a room which does not require air-conditioning can be fully closed by a manual switch. A similar device is disclosed in Japanese Unexamined Utility Model Publication No. 87949/1976 as a fourth prior art reference.
There is Japanese Unexamined Patent Publication No. 169525/1982 as a fifth prior art reference. This prior art is directed to improve cooling air sense at the time of cooling. While the total air volume in the duct is held at a constant level, the air volume is successively delivered to a plurality of outlet ports by operating the dampers so that each outlet port feeds the air into the room intermittently. The damper operation in the fifth prior art is not carried out for the purpose of controlling the room temperature.
There is Japanese Examined Utility Model Publication No. 26056/1973 as a sixth prior art reference. This prior art describes that when on-off control type of dampers all are going to be closed, a specific damper is forcibly opened to prevent all the dampers from being closed simultaneously.
By the way, in order to carry out cooling operation and heating operation by a single device or a single system, a heat pump, the combination of a heat pump and a gas furnace, and the combination of an air conditioner and a gas furnace and so on have been proposed. Selecting the cooling operation and the heating operation is, in general, done by switching a manual switch.
Although, in principle, the cooling operation is selected in summer and the heating operation is selected in winter, frequent switching operations can be required. For example, at the turn of a season, one day needs heating and the next day needs cooling. In the region having a continental climate, there is a case that a night time requires heating though a day time requires cooling. In these cases, if the switching of the cooling and heating operation is not done adequately, comfortable air-conditioning (cooling and heating) can not be obtained.
Some proposals have been offered to automatize the cooling and heating switching control for an air conditioner wherein a room is air-conditioned by a single heat source device. One of the proposals is disclosed in Japanese Examined Utility Model publication No. 9460/1987 as a seventh prior art reference. This prior art discloses that the room temperature T.sub.R is compared to preset reference temperatures T.sub.1, T.sub.2 and T.sub.3 (T.sub.1 &lt;T.sub.2 &lt;T.sub.3), and that when T.sub.R is higher than T.sub.2 at the time of turning on the power, a cooling operation mode is selected, while when T.sub.R is lower than T.sub.1 at the time of turning on the power, a heating operation mode is selected. After that, if T.sub.R becomes lower than T.sub.1, the cooling operation mode is shifted to the heating operation mode, while T.sub.R becomes higher than T.sub.3 the heating operation mode is shifted the cooling operation mode.
In addition, Japanese Examined Patent Publication No. 14694/1984 as an eighth prior art reference discloses a similar device. This device has a first control mode wherein when the room temperature is higher than a target temperature, cooling is selected and when the room temperature is lower than the target temperature by a predetermined value, heating is selected, and a second control mode wherein when the room temperature is lower than the target temperature, heating is selected and when the room temperature is higher than the target temperature by a predetermined value, cooling is selected. When the room temperature is higher than the target temperature at the time of starting the device, the device is controlled under the first control mode. When the room temperature is lower than the target temperature at that time, the device is controlled under the second control mode. When the room temperature has approached the target temperature during the heating operation under the first control mode, the first control mode is shifted to the second control mode to continue to control the device under the second control mode. When the room temperature has approached the target temperature during the cooling operation under the second control mode, the second control mode is shifted to the first control mode to continue to operate the device under the first control mode.
Japanese Unexamined Patent Publication No. 272544/1986 has a ninth prior art reference and Japanese Examined Patent Publication No. 25933/1984 has a tenth prior art reference which disclose similar devices.
It has been known to automatize the cooling and heating switching control for a duct type of air conditioner wherein a single heat source device is utilized and a plurality of rooms are provided with thermostats to regulate the room temperature in each room by the corresponding thermostats. An example is U.S. Pat. No. 4530395 as an eleventh prior art reference. It discloses that each thermostat is provided with a switch for changing cooling and heating and a setting device for setting a set room temperature for cooling and a set room temperature for heating, and that a monitor compares a demand for cooling or heating from each room thermostat with one another to select an operation mode based on the results of comparison, thereby controlling the damper of a room that requires the same operation mode as that selected by the monitor to regulate the temperature in the room while closing the dampers of other rooms.
With regard to the control system as disclosed in the first prior art reference wherein the ventilating operation is carried out while opening all dampers, there is a first problem in that the ventilating air is fed into a room without an occupant to increase the expense for driving the air blower.
Although the system wherein the dampers are automatically controlled depending on the ventilating air temperature is effective in the case of the intake of sufficient volume of the external air, it is not effective when the intake volume of the external air is small and the room temperature control by the external air is difficult in the houses and so on. This is a second problem.
With regard to the air conditioner as disclosed in the second prior art reference, the temperature distribution in a room on heating can be improved and the room temperature can be controlled to reach a set temperature. However, when the number of the dampers is small and the dampers are controlled to be fully opened and fully closed, the case wherein all dampers are fully closed simultaneously happens frequently. In each case, it is necessary to stop the heat source device and the air blower and then restart them. As a result, the deviation in the room temperature from the set temperature and the number of the on and off of the heat source device are increased. This is a third problem.
In particular, the third problem usually happens to the domestic system because the number of rooms is small, a forcible ventilation is not usually done and a heat load is small.
As for the air conditioner as described in the third and fourth prior art references, it is possible to prevent the heat source device and the air blower from being frequently stopped because the dampers are carried out to have a full-open state or a semi-open state. However, when the heat load is small, it is difficult to control the room temperature precisely to become the set temperature, leading to a situation wherein the room temperature is beyond the set temperature on heating. This is a fourth problem.
In respect of the air conditioner as described in the sixth prior art reference, when all dampers are going to be closed, a specific damper is forcibly opened. As a result, it is impossible to control the temperature in the room with the damper forcibly opened to achieve the set temperature desired, and it is against energy-saving. This is the fifth problem.
In reference to the air conditioner as disclosed in the seventh through the tenth prior art reference, their control systems are effective when a single thermostat is used to air-condition a single room. However, when the temperatures in a plurality of rooms are controlled by thermostats, these systems are not applicable because the set temperatures for the rooms are different from one another. This is a sixth problem.
With regard to the air conditioner of the eleventh and the twelfth prior art references, although switching the cooling operation and the heating operation for the entire system can be automatically carried out, selecting the cooling operation and the heating operation in each thermostat must be carried out manually, which is troublesome. This is a seventh problem.